Studies in neurological patients with lesions suggest that the normal process of retrieving words which denote actions depends on regions in left premotor/prefrontal cortex. The aim of this project is to further the understanding of the neural basis of the lexicon, as it pertains to actions and spatial relationships. We will test four principal hypotheses in a series of [150]H2O PET experiments conducted in 45 normal native English speaking adults: (1) The retrieval of words for actions depends on neural structures partially segregated from those underlying retrieval of words for concrete entities. (2) The retrieval of words for actions performed with manipulable artifacts depends on neural structures partially segregated from those underlying the retrieval of words for actions performed without such artifacts. (3) The neural substrate for the retrieval of words for actions is independent of the sensory modality in which the action stimulus is presented (e.g., visual [pictures] versus auditory [associated sounds]). (4) The retrieval of words which denote spatial relationships depends on neural structures partially segregated from those underlying retrieval of words for concrete entities or actions. In the experiments planned to address these hypotheses, we expect to uncover the neural structures underlying various aspects of spoken language, so as to shed eight on the normal physiology of language processing which may be used in the evaluation of subjects with language deficits such as aphasias, and in conjunction with Project 2, also to help understand language processes in deaf and hearing impaired individuals. Such knowledge may ultimately be of help in the search for ways to improve the understanding of language processing by deaf signers, and inform the development of rehabilitation strategies for individuals with acquired language disorders such as aphasias.